1. Field of the Invention
The present invention relates to a electrophotographic photosensitive member having a deposited film made of a non-single-crystal material on a cylindrical substrate, and more particularly to an electrophotographic photosensitive member which can stably provide an image with high quality for a long period without generating an image dimness and an image smearing under a severe environment such as a high temperature and a high humidity even when the heating means of the electrophotographic photosensitive member is not provided in all electrophotographic processes, and further without generating imperfect cleaning or fusion under all environments.
2. Related Background Art
A non-single-crystal deposited film made of a non-single-crystal silicon (a-Si) or the like compensated by hydrogen and/or halogen (for instance, fluorine, chlorine, etc.) has been proposed and put to practical use as a pollution-free photosensitive member with high performance and high durability. The a-Si photosensitive member has a higher surface hardness than other photosensitive members, exhibits a high sensitivity to a;wavelength light such as a semiconductor laser (600 nm to 700 nm) and the deterioration of the potential characteristic thereof due to repeated use is hardly recognized, so that the a-Si photosensitive member has been widely employed particularly for the electrophotographic photosensitive member of a high speed copying machine or a LBP (laser printer).
With the recent increase of information throughput, a demand for the high speed copying machines or the LBPs has been further increased and the amount of copying for each copying machines has been excessively augmented.
Under these circumstances, the durability of the electrophotographic photosensitive member and the decrease of the deterioration of its potential characteristic due to repeated use have been more requested than before. In order to meet this request, various kinds of studies of the surface layer of the a-Si photosensitive member have been specially carried out. Especially, in recent years, a non-single-crystal carbon (a-C) film has been proposed as a material of the surface layer of the a-Si photosensitive member.
Japanese Patent Application Laid-Open No. 61-219961 discloses a technique that a material composed of a hydrogenated non-single-crystal carbon and 10 to 40 atomic % of hydrogen atom is employed as a surface layer. In accordance with these techniques, electrical, optical and photoconductive characteristics, an environmental characteristic for use and a durability can be improved and further, an image quality can be improved.
Further, Japanese Patent Application Laid-Open No. 6-317920 discloses a method for producing a surface layer made of a non-single-crystal carbon material including carbon,atoms as a matrix by plasma CVD for decomposing feed gas by a glow discharge generated by an electromagnetic wave with frequency of 20 MHZ to 450 MHZ.
When the above described a-Si photosensitive members are applied to the electrophotographic apparatus, an electric latent image is formed on the photosensitive member by charging, discharging and exposure means. Then, the latent image is developed by using a developer (toner), and a toner image is transferred to a transfer material such as a sheet if necessary. After that, the toner image is fixed to the transfer material by heating, pressing, and heating and pressing or solvent steam or the like to obtain a copied product. Further, the toner which is not transferred but remains on the photosensitive member is recovered in a cleaning process and exhausted outside as a waste toner.
As charging and discharging means of the photosensitive member, a corona charger (Corotron, Scotron) is used in most cases. However, in accordance with a corona discharge, ozone (O3) is generated to oxidize nitrogen in air and produce corona discharge products such as nitrogen oxides (NOx). Further, the produced nitrogen oxides react with water content in the air to undesirably produce nitric acid or the like to lower the resistance on the surface of the photosensitive member.
Therefore, a transverse charge holding capacity is entirely or partly lowered so that there is generated a defective image called an image dimness or an image smearing (an electric charge on the surface of the photosensitive member leaks in the direction of a plane so that an electrostatic latent image pattern collapses or is not formed).
In addition, since the corona discharge product adhering to the inner surface of the shield plate of the corona discharger stains the surface of the photosensitive member not only during the operation of the electrophotographic apparatus but also during the stop of the apparatus at night, the image dimness and the image smearing are apt to be generated in areas corresponding to the aperture of the charger during the stop of the apparatus on a first sheet or several hundreds of sheets which are outputted upon restart of the apparatus after the apparatus stops. The above described image smearing looks like the trace of the charger, hence it is referred to as a charger trace smearing.
Further, in case of the a-Si photosensitive member, since the surface hardness thereof is higher than that of other photosensitive members, which reversibly acts, the corona discharge product adhering to the surface of the photosensitive member is liable to remain indefinitely. Thus, there have been proposed two following methods for preventing the image dimness or the image smearing phenomenon.
According to the first method, a heater for heating the photosensitive member itself is housed, or hot air is supplied to the photosensitive member by a hot airblower to heat the surface of the photosensitive member at 30 to 50xc2x0 C. so that a relative humidity is lowered. This method is a treatment for volatilizing the corona discharge product or moisture sticking to the surface of the photosensitive member to substantially prevent the resistance on the surface of the photosensitive member from being decreased and is put to practical use.
According to the second method, a water repellency on the surface of the photosensitive member is improved so that the corona discharge product hardly sticks to the surface of the photosensitive member from the start, and accordingly the image smearing is prevented. For example, Japanese Patent Application Laid-Open No. 61-289354 discloses the a-C surface layer obtained by applying plasma treatment to a surface with gas including fluorine. Further, Japanese Patent Application Laid-Open No. 61-278859 discloses a method for manufacturing an electrophotographic photosensitive member having a surface layer composed of a-C:H on an a-Si photosensitive layer and specifying a self-bias.
In the meantime, as for a development, toner usually having weight average particle size of about 10 to 12 xcexcm is often used. Nowadays, however, a more minute and delicate image quality is required, so that the toner of small particle size is needed and the development thereof is hastened.
A capability for fixing the toner image to the transfer material depends on how the toner image on the transfer material is heated in a fixing device. For a speed-up operation, is developed a technique that a fixing characteristic is improved by a low melting point toner.
However, when the fixing characteristic is improved, there occurs a fear that the toner tends to stick to the surface of a drum to form a defective image. Thus, in order to make it difficult for the toner to stick to the photosensitive member, it is necessary to enhance the sliding characteristic of the surface of the photosensitive member as well as a cleaning characteristic for mechanically scraping the toner sticking to the surface of the photosensitive member.
As cleaning. means, are extensively employed a blade type cleaning system with a high cleaning capability and a magnetic roller (a cleaning roller formed with a magnetic brush) or the like in combination.
As methods for meeting a change to the small size of the toner and the high fixing characteristic or the like, are considered countermeasures that the hardness of a blade is raised, the pushing pressure of the blade is increased, and the rotating speed or the rotating direction of the magnetic roller (a forward direction or a reverse direction relative to the photosensitive member) is changed. The fusion and the slip or fall of the toner are prevented on the basis of these countermeasures.
However, according to a method of heating the surface of the photosensitive member to 30 to 50xc2x0 C. by a heater in order to prevent the image smearing as described above, the consumed power of a copying machine matrix is undesirably increased. Therefore, it may be possibly difficult to operate high speed copying machines within a power of 100V/15 xc3x85, which is the state of a power supply generally employed in ordinary offices.
Further, the heater for heating the photosensitive member cannot be turned off even at night, for the purpose of suppressing the image smearing on the first sheet to several hundreds of sheets upon restart due to ozone products falling and accumulated from the charger during the night. Therefore, an improvement has been desired from the recent energy saving and ecological point of view.
Further, a method of the above described methods for preventing the image smearing by which the corona discharge product seldom sticks to the surface of the photosensitive member from start by improving the water repellency on the surface of the photosensitive member has still a problem to be solved in view of durability. Therefore, the surface of the photosensitive member which is originally rich in durability must have a desired durability of higher level. Accordingly, the conventional electrophotographic apparatus has such problems to be solved as to provide a good image without providing the heating means of the photosensitive member and to eliminate the variation of an image characteristic due to repeated use.
The improvement of the surface feature of the photosensitive member and the cleaning characteristic of the electrophotographic apparatus permits an electrophotographic image to obtain an image quality higher than that obtained so far. However, the improvement of the cleaning characteristic may possibly increase the amount of shaving of the surface of the photosensitive member more than that got hitherto with disadvantage.
Especially, when a-C:F film containing fluorine is used for the surface layer, the sliding characteristic of the surface of the photosensitive member is improved due to fluorine contained in the film. However, this surface becomes softer than that using the a-C film and is more liable to be scraped. Therefore, there occurs sometimes a problem in view of stability due to the repeated use of the photosensitive member.
Accordingly, even in the electrophotographic process whose cleaning characteristic is enhanced, the achievement of a more improved stability in the repeated use of the drum has been required without scraping the drum.
The present invention has been accomplished by taking the above mentioned problems into consideration and it is an object of the present invention to provide an electrophotographic photosensitive member excellent in its repeated use in an electrophotographic apparatus and an electrophotographic apparatus having the above photosensitive member.
It is another object of the present invention to provide an electrophotographic photosensitive member capable of providing a stable image in which an image dimness or an image smearing or the like is not generated irrespective of an environment even when heating means are not provided and an electrophotographic apparatus having the above described electrophotographic photosensitive member.
It is still another object of the present invention to provide an electrophotographic photosensitive member excellent in its cleaning characteristic even when a toner having a small particle size and an excellent fixing characteristic is used, and in which a problem resulting from the fusion of the toner is not generated, or is negligible and an electrophotographic apparatus having the above described photosensitive member.
In addition, it is still another object of the present invention to provide an electrophotographic photosensitive member comprising: a photoconductive layer comprising a non-single-crystal material containing silicon atoms as a matrix on a cylindrical substrate; a first surface layer comprising a non-single-crystal material; and a second surface layer comprising a non-single-crystal carbon containing at least fluorine, these layers being successively formed in this order, wherein hardness of the first surface layer is larger than that of the second surface layer and the center line average surface roughness (Ra) of the first surface layer is 50 xc3x85 to 5000 xc3x85, and an electrophotographic apparatus having the above described photosensitive member.